Small-molecule metabolites modulate various components of life. In some instances, their biological functions are mediated and regulated by interactions with proteins. In some cases, these metabolite-protein interactions include ligand-receptor, substrate-enzyme, and client-carrier relationships, many of which represent key nodes in biochemical networks that regulate cell physiology and disease. Eukaryotic and prokaryotic cells harbor numerous structurally distinct metabolites. Among these natural products, lipids display a capacity to interact with and to affect the functions of proteins.